Semiconductor devices, in particular memory devices such as DRAMS (DRAM=Dynamic Random Access Memory or dynamic read-write-memory, respectively) in general comprise one or several voltage supply means.
A voltage supply means serves to generate, from an—externally provided—voltage, a voltage used internally in the semiconductor device.
The voltage level of the internal voltage generated by the semiconductor device voltage supply means may differ from the level of the external voltage.
In particular, the internally used voltage level may be lower than the externally used voltage level.
An internal voltage level that is reduced vis-à-vis the externally used voltage level has, for instance, the advantage that the power loss in the semiconductor device can be reduced.
Furthermore, the external voltage may be subject to relatively strong fluctuations. Therefore, a so-called voltage regulator is frequently used as voltage supply means, which—in order that the device may be operated without fault—converts the external voltage into an internal voltage that is subject to relatively minor fluctuations only and is regulated at a particular, constant (possibly reduced) value.
Conventional voltage regulators may, for instance, comprise a differential amplifier and a field effect transistor. The gate of the field effect transistor may be connected to an output of the differential amplifier, and the source of the field effect transistor may e.g. be connected to the external voltage.
A reference voltage—which is subject to relatively minor fluctuations only—is applied to the positive input of the differential amplifier. The voltage output at the drain of the field effect transistor may be fed back to the negative input of the differential amplifier directly, or e.g. by the interposition of a voltage divider.
The differential amplifier regulates the voltage available at the gate connection of the field effect transistor such that the (fed back) drain voltage—and thus the voltage output by the voltage regulator—is constant and as high as the reference voltage, or e.g. by a certain factor higher.
Semiconductor devices are usually incorporated in appropriate housings, e.g. appropriate surface mountable housings (SMD housings) or plug mountable housings (e.g. corresponding Dual-In-Line (DIL) housings, Pin-Grid-Array (PGA) housings, etc.).
In one single housing, there may also be arranged two or more semiconductor devices instead of only one single semiconductor device.
In the case of memory devices, in particular DRAMs for increasing the storage density, several semiconductor devices may, for instance, be mounted in a stacked manner in one single housing.
For instance, two 256 Mbit memory devices may be provided in one single housing, this effecting a 512 Mbit chip.
The semiconductor devices, in particular memory devices, provided in one single housing comprise voltage supply means that are independent of one another.
When a memory device is accessed (i.e. when corresponding external data are stored on the memory device, or when data that are stored on the memory device are read out), there will flow, in general, relatively high currents that are generated by the corresponding voltage supply means.
Contrary to this, only relatively low currents will flow in standby or refresh operaation (e.g. for supplying leakage currents or operating currents).
The standby or refresh currents each may, for instance, be in the range of apporx. 50 μA—i.e. amount to a total of 100 μA in the case of e.g. two stacked memory devices (with the operating currents of the respective voltage supply means constituting the major part of these currents).